Important points to remember :
- All substances are made up of very small particles. Objects are made up of substances. Objects have a specific shape, their parts have a specific arrangement, by which we identify them. We use wood, plastic or steel, to make a table, chair or cupboard.
- These substances have the strength required to make these articles.
- Glass can be made from sand and calcium carbonate. However, sand and calcium carbonate cannot be obtained again from glass.
- Rubber is a natural substance obtained by collecting the latex of a certain tree. Rubber trees are found in abundance in Brazil.
- We use two types of materials – natural and man-made. Natural materials may be biotic or abiotic. Biotic materials are either of plant origin or animal origin.
- Rubber, paper and synthetic fibres are important man-made materials in our daily use.
- Man-made materials are obtained by using certain processes.
Question 1: Fill in the blanks using proper words.
a) Rubber made by vulcanization is a man-made material.
b) Man-made materials are made by processing natural materials.
c) Nylon thread was developed simultaneously in New York and London.
d) Rayon is also known as synthetic silk.
Question 2: Answer the following questions.
a) Why did the need for man-made materials arise?
Answer : For several years, humans have been dependant on natural materials to meet their demands. However, there has been a shift towards the use of man made materials as well. Increasing population, deforestation and limited natural resources are some of the reasons due to which the need for man made materials arised. Another reason which led to the increase in the use of man made material was to get a comfortable lifestyle.
b) Which are the natural materials obtained from plants and animals?
Answer : Wood (rattan, bamboo, bark, etc.) Natural fiber (silk, wool, cotton, flax, hemp, jute, kapok, kenaf, moss, etc.) Inorganic material. Stone (flint, granite, obsidian, sandstone, sand, gems, glass, etc
c) What is Vulcanization ?
Answer : It is the process carried out for the production of rubber. In this process, raw rubber is heated with a mixture of sulphur and an appropriate additive, at a temperature range of 61.85Unknown node type: sup C to 141.850C for three to four hours. Sulphur is added to give toughness to rubber.
d) Which natural materials are used to obtain fibres?
Answer : Natural materials obtained from plants and animals are used to obtain fibers. For example, wool and silk are natural materials of animal origin which are used for obtaining fibers. Wool is obtained from the fleece (hair) of sheep or yak and silk is obtained from the cocoons of a silk moth. Cotton and jute are examples of natural materials of plant origin which are used for obtaining fibers.
Question 3: What are we used for ?
a. Soil- It is used in construction, pottery, medicine and cosmetics.
b. Wood- It is used in making furnitures, as a source of fuel, utensils, hand tools, musical instruments, wooden toys etc.
c. Nylon- It is used in making canopies of parachutes, tents, sleeping bags, sails, rope, tennis strings, fishing poles and lines, cookware etc.
d. Paper- It is used in making bags, envelopes, notebooks, packaging purpose etc.
e. Rubber- Balloons, erasers, rubber toys, rubber balls etc.
Question 4: How is paper manufactured? Write in your own words.
Answer: Paper is manufactured by the following process:
- Logs of wood are made to pass through a debarker, where the barks of the tree are separated.
- Then the wood is chopped into small pieces and is mixed with some chemicals and water in digetser for the formation of the pulp.
- The obtained pulp is washed refined and sometimes even bleached.
- The pulp is made to travel down the screen to remove excess of water and then to the rollers where it is being dried and squeezed between large rollers to form rolls of paper.
Question 5: Give scientific reasons.
a) We must use cotton clothes in summer
Answer : We must use cotton clothes in summers because they protect us from the heat of the sun. They absorb sweat and help keep our bodies cool. The pores in cotton clothes allow the free movement of air, which helps cool our bodies.
b) We must observe economy in the use of materials.
- We must observe economy in the use of materials because they directly or indirectly affect our environment. Most of the natural materials which we obtain from our environment are exhaustible/non renewable resources i.e. once these resources are finished they cannot be renewed again or even if they can, it would take several years to do so.
- For example, our forests from where we obtain wood are precious resources because once a forest is destroyed, it would take several years to renew that forest. Also, destroying the forests for our needs affects the habitat of several other species of organisms and plants.
- The man made materials which we use are largely non biodegradable for example plastic etc. Increased use of man made materials pose a threat to the environment because their disposal is not easy and leads to environmental pollution.
- These examples state the importance of judicious use of both natural and man made materials.
c) Saving paper is the need of the hour.
- We very well know that paper is obtained from trees. Trees are important resources because they not only provide us with wood or paper but are also a habitat for various organisms.
- They are important in maintaining the climate as well.
- The more paper we use or waste, the more no. of trees will have to be cut down for this purpose, thus leading to various kinds of harmful effects on our environment.
- We should make a genuine effort in saving paper by adopting small steps which can make a huge difference.
d) Man-made materials have more demand
Answer : Man made materials have more demand because of their characteristics like easy to use, low cost of production, cheaper products and variety of things which can be made from them.
e. Humus is a natural material.
Answer : Humus is a natural material because its formation is a natural process. It is the dark-coloured layer of top soil that is rich in nutrients. The decomposers convert the dead plants and animals into humus that is utilised by the plants. It increases the fertility of the soil.
Question 6: Find out.
a) How is lac obtained from nature?
Answer : Lac is a natural resin and is a product of animal origin. It is secreted by an insect, known as lac-insect. In order to obtain lac, these insects are cultured and the technique is called lac-culture. Lac culture requires proper care of host plants, regular pruning of host plants, propagation, collection and processing of lac.
The lac insect lives as a parasite, feeding on the sap of certain trees and shrubs. Lac secretion begins as soon as the larva of the insect settles on the plant. Intially, lac has a shining appearance but later on it turns harder on coming in contact wih air.
This lac is then collected and used for making jewellery etc.
b) How are pearls obtained?
Answer : Pearls are precious jewels and the only gems created by a living animal. They are formed when a microscopic foreign object finds its way inside a mussel or oyster.
The animal coats the object with a substance called nacre. With time, several layers of nacre build up over the foreign material thus leading to the formation of a pearl. These oyesters/mussels are collectd from the sea and opened to collect these pearls.
# Can you tell :
1) What is the difference between these two groups of natural substances – leather, jute, wool, cotton and water, soil, metals.
Answer : A natural material happens to be any product or corporeal matter whose origins are animals, plants, or the soil. Talking about leather, wool, jute, cotton and soil, water, metals, the origins of all of these are animals, plants, or the soil.
As to how metals belong to this category the explanation is the vertical allotment of permissible limit of heavy metals in soil profiles and it’s the outcome of accumulation and migration of heavy metals under the mixed influence of environmental conditions and edaphic factors
2) From which substances in nature can we get threads or fibre?
Answer : Fibers used to make industrial sewing threads come from two major sources: Natural Fibers- Come from plants or animals and are spun or twisted into yarns. Cotton is the most common natural fiber used to make thread. Other natural fibers include rayon, silk, wool, jute, ramie, hemp, and linen.
3) What are clothes made from?
Answer : Clothes are made from lots of different materials. Some materials, like leather, are made from animal skins. Cotton and linen are made from plants. Other materials, such as polyester, are called ‘man-made materials.
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